In my U.S. Pat. No. 4,498,827 there is described a turnbuckle device which finds wide use for retaining tarpaulins or the like in position. In such use the tarpaulin is provided with a grommet having an elongated opening through which the head of the turnbuckle may be passed when aligned with the major axis of the grommet, and which is trapped when the head is rotated through 90 degrees. Elongated grommets of the foregoing nature must be specifically manufactured and applied to the tarpaulin, whereas round grommets are relatively cheap and more readily applied.